In the development of new generations of semiconductor components, in particular of vertical power semiconductor components, reducing the specific on-resistance Ron is very important. By reducing the resistance it is possible firstly to minimize the static power loss and secondly to provide power semiconductor components having a higher current density. It is thereby possible to use significantly smaller and hence more cost-effective semiconductor components for the same total current.
One approach used to reduce the on-resistance is to use semiconductor components having trench structures instead of planar cell structures. In the case of such components, trenches are introduced into the semiconductor region, with vertically oriented gate electrodes being introduced into the trenches. Such semiconductor components have a larger channel width per unit area, as a result of which the on resistance Ron is significantly reduced. Particularly in the case of power semiconductor components, however, the influence of the resistance brought about from a drift zone on the total on resistance is particularly great. In order to reduce the on resistance, semiconductor structures having deep trenches are preferably used. The deep trenches adjoin the body zone or the channel zone in the upper region and project far into the drift zone in the lower region. The deep trenches have inside them a dielectric embodied in a step-like manner, the dielectric being made thicker in the lower region of the trench than in the upper region. In the upper region of the trench, the dielectric holds the gate oxide for channel control. In the lower region, the dielectric, typically embodied as a field oxide, serves for insulating a field plate from the semiconductor region.
WO 01/08226 A2 and WO 01/71817 A2 in each case describe trench MOSFETS having electrodes which are arranged in a trench extending into a semiconductor region. The electrodes are surrounded by a thicker insulation layer in the lower region than in the upper region of the trench, as a result of which the electrodes serve, in the upper region, upon a driving potential being applied, as a gate electrode for forming a conductive channel in an adjacent body zone and, in the lower region, as a field plate. The alignment of the gate electrodes with respect to the pn junctions of the body zone is of crucial importance for the reliable formation of a channel through the body zone. This is because if the pn junction does not lie in the region of influence of the gate electrode, it is not possible to form a channel extending over the entire body region as far as the respective pn junction. In particular, the optimization of a semiconductor component with regard to parasitic gate-source or gate-drain capacitances requires the gate electrodes to be aligned as precisely as possible with respect to the pn junctions in order, on the one hand, to have the smallest possible overlap between the gate electrode and the source or drain region, but on the other hand to provide for the reliable formation of a channel over the entire body region as far as the respective pn junctions. On account of fabrication tolerances during so-called recess etching of the structures in the trench of a trench MOSFET, this alignment is not possible in an optimal fashion.